Most people infected by the Japanese encephalitis virus have either no symptoms, or mild symptoms that are short-lived and flu-like (e.g fever and headache). Hence, people often underestimate these symptoms.
In less than 1 in every 250 cases, the infection may spread to the brain and cause more serious symptoms, such as:
- High fever
- Seizures (fits)
- Paralysis (inability to move certain body parts)
- Neck stiffness
The case-fatality rate can be as high as 30% among those with disease symptoms.
Of those who survive, 20%–30% suffer permanent intellectual, behavioral or neurological problems such as paralysis, recurrent seizures or the inability to speak.